Prevalence of Chronic Q Fever in Patients with a History of Cardiac Valve Surgery in an Area Where Coxiella burnetii Is Epidemic

Abstract

ABSTRACTChronic Q fever develops in 1 to 5% of patients infected withCoxiella burnetii. The risk for chronic Q fever endocarditis has been estimated to be ∼39% in case of preexisting valvulopathy and is potentially even higher for valvular prostheses. Since 2007, The Netherlands has faced the largest Q fever outbreak ever reported, allowing a more precise risk estimate of chronic Q fever in high-risk groups. Patients with a history of cardiac valve surgery were selected for microbiological screening through a cardiology outpatient clinic in the area where Q fever is epidemic. Blood samples were analyzed for phase I and II IgG againstC. burnetii, and if titers were above a defined cutoff level,C. burnetiiPCR was performed. Chronic Q fever was considered proven ifC. burnetiiPCR was positive and probable if the phase I IgG titer was ≥1:1,024. Among 568 patients, the seroprevalence ofC. burnetiiantibodies (IgG titer greater than or equal to 1:32) was 20.4% (n= 116). Proven or probable chronic Q fever was identified among 7.8% of seropositive patients (n= 9). Valve characteristics did not influence the risk for chronic Q fever. Patients with chronic Q fever were significantly older than patients with past Q fever. In conclusion, screening of high-risk groups is a proper instrument for early detection of chronic Q fever cases. The estimated prevalence of chronic Q fever is 7.8% among seropositive patients with a history of cardiac valve surgery, which is substantially higher than that in nonselected populations but lower than that previously reported. Older age seems to increase vulnerability to chronic Q fever in this population.